How to horizontally center an element

You can apply this CSS to the inner <div>:

#inner {
  width: 50%;
  margin: 0 auto;
}

Of course, you don't have to set the width to 50%. Any width less than the containing <div> will work. The margin: 0 auto is what does the actual centering.

If you are targeting Internet Explorer 8 (and later), it might be better to have this instead:

#inner {
  display: table;
  margin: 0 auto;
}

It will make the inner element center horizontally and it works without setting a specific width.

Working example here:

#inner {
  display: table;
  margin: 0 auto;
  border: 1px solid black;
}

#outer {
  border: 1px solid red;
  width:100%
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

EDIT

With flexbox it is very easy to style the div horizontally and vertically centered.

#inner {  
  border: 1px solid black;
}

#outer {
  border: 1px solid red;
  width:100%;
  display: flex;
  justify-content: center;
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

To align the div vertically centered, use the property align-items: center.

If you don't want to set a fixed width on the inner div you could do something like this:

#outer {
  width: 100%;
  text-align: center;
}

#inner {
  display: inline-block;
}

<div id="outer">  
    <div id="inner">Foo foo</div>
</div>

That makes the inner div into an inline element that can be centered with text-align.

The best approaches are with CSS 3.

Box model:

#outer {
  width: 100%;
  /* Firefox */
  display: -moz-box;
  -moz-box-pack: center;
  -moz-box-align: center;
  /* Safari and Chrome */
  display: -webkit-box;
  -webkit-box-pack: center;
  -webkit-box-align: center;
  /* W3C */
  display: box;
  box-pack: center;
  box-align: center;
}

#inner {
  width: 50%;
}

<div id="outer">
  <div id="inner">Foo foo</div>
</div>

According to your usability you may also use the box-orient, box-flex, box-direction properties.

Flex:

#outer {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    justify-content: center;
    align-items: center;
}

Read more about centering the child elements

• Link 2

• Link 3

• Link 4

And this explains why the box model is the best approach:

• Why is the W3C box model considered better?